1. Field of the Invention
The present invention relates to an internal combustion engine having a thermal storage device.
2. Description of the Related Art
Demands for improvement of startability, reduction of fuel consumption and improvement of emission are placed on internal combustion engines that are in a cold state. To meet these demands, there is a known technology utilizing a thermal storage device as a technology for heating the internal combustion engine in an early stage (see for example, Japanese Patent Application Laid Open No. 2002-21560). In this technology, cooling fluid in a cooling device is utilized. Specifically, according to this technology, a portion of the cooling fluid that has been heated during running of the engine is stored in a thermal storage tank while keeping its heat even after the engine has been stopped, and the warm cooling fluid is returned to the engine before starting the engine. (In the following description, the operation of returning heated cooling fluid to the engine before starting it will be referred to as “preheat process”.)
Here, an example of an internal combustion engine having a thermal storage device according to a related art will be described with reference to FIGS. 1 and 2. FIGS. 1 and 2 are schematic diagrams showing an internal combustion engine having a thermal storage device according to a related art. The arrows in FIG. 1 indicate flows of cooling fluid that serves as heat medium during the preheat process. The arrows in FIG. 2 indicate flows of cooling fluid while the engine is running.
As shown in these drawings, the internal combustion engine having a thermal storage device 200 has an engine main body 210 including a cylinder head 211 and a cylinder block 212, a thermal storage tank 220 for storing a portion of the cooling fluid serving as heat medium that has been heated by the engine main body 210 while keeping its heat, an electric pump 230 for causing the cooling fluid to flow out of the thermal storage tank 220, a mechanical pump 240 driven by a belt (not shown) provided in the engine main body 210, a three-way valve 250 for switching the flow path through which the cooling fluid runs, a heater core 260 used for heating the vehicle cabin and a radiator 270 for cooling the cooling fluid.
With the above-described structure, when the preheat process is performed, the electric pump 230 is turned on. At that time, the valve in the three-way valve 250 that leads to the heater core 260 is closed. Accordingly, the cooling fluid flows along a circulative flow path running through the thermal storage tank 220, the cylinder block 212 and the cylinder head 211 as shown in FIG. 1. Thus, warm cooling fluid stored in the thermal storage tank 220 is supplied to the cylinder block 212 and the cylinder head 211. As per the above, since the cylinder block 212 and the cylinder head 211 are heated before starting the engine, the engine warm-up process is facilitated. Afterward, the electric pump 230 is turned off, and the preheat process is terminated.
While the engine is running, the mechanical pump 240 is operated. In that time, the valve in the tree-way valve 250 that leads to the thermal storage tank 220 is closed. Accordingly, the cooling fluid flows along a circulative flow path running through the engine main body 210 and the heater core 260 and along a circulative flow path running through the engine main body 210 and the radiator 270, as shown in FIG. 2. Thus, cooling fluid warmed by the engine main body 210 is supplied to the heater core 260 and the radiator 270. Consequently, the heater core 260 and the radiator 270 are heated, and the heat of the cooling fluid is removed by the heater core 260 and the radiator 270.
There is a known method of cooling during the engine running, that is, the U-turn cooling system in which cooling fluid is supplied to the cylinder block from one end of the engine main body, and then supplied to the cylinder head after flowing by way of the other end (see, for example, Japanese Patent Application Laid-Open No. 7-224651). Some known internal combustion engines that utilize the U-turn cooling system are further provided with a flow path for feeding the cooling fluid supplied to the cylinder block from one end of the engine main body directly to the cylinder head. The main reason why the flow path for supplying the heat medium to the cylinder head after the U-turn travel in the cylinder block and the flow path for feeding the heat medium directly from the cylinder block to the cylinder head are provided is that the demand for cooling is stronger in the cylinder head than in the cylinder block in the internal combustion engine. In this connection, the internal combustion engine shown in FIGS. 1 and 2 is provided with the two types of flow paths for cooling mentioned here.
In such internal combustion engines 200 provided with two types of cooling fluid flow paths, when cooling fluid is supplied to the engine main body 210 from the thermal storage tank 220 in the preheat process also, cooling fluid is supplied to the cylinder block from the one end of the engine main body using the flow paths same as those used in supplying cooling fluid while the engine is running.
In the preheat process, it is considered to be more effective that the cylinder block be heated earlier than the cylinder head in reducing frictions in various sliding portions and in improving gas mileage.
An object of the present invention is to enhance the efficiency of heating of the cylinder block by a thermal storage device.
Another object of the present invention is to reduce fuel consumption.